The present disclosure relates generally to systems and methods for bottom hole pressure control.
Earth formations undergo geological changes which result in unexpected pressure and rock strength variations over millions of years. Complex, deep-water and unconventional reservoirs often exhibit wellbore mechanics that prevent use of conventional drilling techniques. Conventional drilling practices have typically maintained the hydrostatic pressure of the drilling fluid in the wellbore between the formation's pore pressure and its fracture pressure. Drilling fluid is continuously circulated within the wellbore to control the formation fluids and transport cuttings to the surface. However, since the drilling fluid pressure is higher than the natural formation pressure, fluid invasion frequently occurs causing permeability damage to the formation, caused by washout of the formation or physical blockage from the intrusion of the fluid into the formation structure itself, resulting in lost circulation of drilling fluid and causing non-productive time.
Managed pressure drilling (MPD) was developed as a group of technologies to more precisely control the annular pressure profile throughout wellbores by creating only a minimal overbalanced annular pressure. MPD involves “low-head” and “at balance” drilling, in which downhole pressure is kept marginally above or equal to the reservoir pore pressure, reducing fluid loss. By ascertaining downhole pressure environmental limits and managing the annular hydraulic pressure profile accordingly, MPD techniques adjust the annular pressure to keep it within desired limits at multiple fixed points in the wellbore while continuously drilling in the wellbore, allowing for drilling through multiple different pore pressure and fracture gradients in the same hole section.
With MPD, there is a need to have precise control on the profile of annular pressure during drilling and cementing. However, current methods using conventional calculations for controlling bottomhole pressures in extended reach wells do not properly take into consideration the elasticity of drill pipes and therefore do not control to the proper pressures. For the foregoing reasons, there is a need for methods of more precisely controlling the annular pressure profile throughout the well bore. By manipulating pressure within the wellbore at multiple depths within the wellbore to better control the annular pressure, several incidents regarding non-productive time can be mitigated, such as differential sticking and lost circulation. MPD also enables possibilities for extending casing points to limit the total number of casings, limiting lost circulation, drilling with total lost returns and increasing the penetration rate.